The proposed research project studies a potential virulence mechanism of Mycobacterium tuberculosis (Mtb), the etiologic agent of tuberculosis (TB). TB is one of the leading worldwide causes of death among adults. One factor contributing to Mtb success as a pathogen is its ability to reside and replicate within the toxic environment of the host macrophage. Among the major antimicrobial products elicited by activated macrophages are reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI). The long-term objective of this project is to improve the understanding of Mtb RNI and ROI resistance as it relates to survival within the host macrophage. Although ROI and RNI are important host defenses against intracellular organisms, some Mtb strains are capable of resisting these toxic products. The high-output pathway of nitric oxide production is a critical element of host defense against TB in mice. In addition, studies have demonstrated that RNI are produced by human alveolar macrophages in TB patients. These findings direct our attention to the molecular genetics and epidemiology of Mtb strains that are better able to resist the deleterious effects of RNI and ROI as well as putative genes that are associated with RNI and ROI resistance. Consequently, the hypotheses being addressed in this study are: 1) differences in susceptibility to RNI and ROI exist among clinical Mtb isolates that may play a role in transmission within specific populations and 2) genetic factors exist within the Mtb genome that are associated with the organisms' ability to survive in the presence of ROI and RNI. In order to test these hypotheses, two specific aims will be addressed. Aim one will analyze RNI and ROI resistance patterns among Mtb isolates from TB patients throughout Louisiana. We will compare ROI and RNI resistance levels among 50 Mtb isolates using in vitro survival assays. In addition, epidemiologic data will be used to identify factors associated with a strain's ability to resist RNI or ROI. This aim will provide a better understanding of the Mtb strains circulating throughout Louisiana; hence, affording the potential to improve treatment, prevention, and intervention strategies. Aim two will further analyze a previously identified factor in Mtb that may be involved in RNI and ROI resistance using allelic exchange techniques. This aim will identify a putative RNI/ROI resistance factor in Mtb; hence, furthering the understanding of Mtb intracellular survival mechanisms. Since both reactive oxygen and nitrogen intermediates are important host macrophage defenses against intracellular organisms, we hypothesize that Mycobacterium tuberculosis has evolved mechanisms that allow the organism to resist these host defenses, ultimately enhancing their ability to survive and replicate within the host and be transmitted to susceptible individuals. The long-term objective of this project is to improve the understanding of M. tuberculosis resistance to reactive oxygen and nitrogen intermediates by identifying specific risk factors for becoming infected with resistant M. tuberculosis strains and to further characterize a novel genetic factor involved in the organisms' growth and survival. Consequently, the proposed study affords the potential to decrease the spread of tuberculosis by improving prevention strategies and identifying novel targets for drugs acting to sensitize the pathogen to the natural antimicrobial actions of the host. [unreadable] [unreadable] [unreadable]